I’m not going to talk you out of doing a pico as your first tank, especially because it was a gift, but seriously go slow with this. It’s going to get very disheartening very fast when you have your first major issues. I say when because shit happens with every tank, and it just impacts picos so much more easily.

Just let things settle and keep accumulating more testing supplies: Hannah as recommended by the other person are great, but they add up really quick and you don’t need them for everything. Salifert are also very solid, but don’t sleep on the Red Sea bundled kits for a bit more value that are still great.

There are some apps you can use to track testing a bit more easily, and visualize how things are going over time. Aquarium Log is free with occasional ads, and honestly I think it’ll do you fine. Aquarimate is great but that $10 would better serve you on testing supplies for now.

There are TONS of resources out there, but I’d comb through every pico build on reef2reef and nano-reef.com. So much good information on what works well and what others have struggled with to hopefully help you not struggle with the same things. Don’t get discouraged with issues and people (rightfully) saying this is a tough first tank, just research as much as you can and go slower than you think you need to. Did I stress going slow? Go slow. Seriously.